Method of recovering carbon dioxide from gas and apparatus therefor

ABSTRACT

Provided is a method including the steps of: cooling exhaust gas to a given temperature by use of cold energy of liquefied natural gas; spraying water in a minute-ice generator having been cooled to a given temperature by use of the cold energy of the liquefied natural gas to generate minute ice; and introducing the minute ice and the cooled exhaust gas into a gas hydrate generator so as to cause the minute ice and carbon dioxide in the exhaust gas to react with each other in the gas hydrate generator, thereby generating carbon dioxide hydrate.

TECHNICAL FIELD

The present invention relates to a carbon dioxide separating andrecovering method that involves: contacting exhaust gas with particulateice at a low temperature by use of cold energy of LNG (liquefied naturalgas) to generate carbon dioxide hydrate; and then fixing carbon dioxide(CO₂) in the exhaust gas to the gas hydrate, thereby recovering thecarbon dioxide from the exhaust gas, and also relates to an apparatustherefor.

BACKGROUND ART

Recently, methods of recovering carbon dioxide (CO₂) included in exhaustgas are developed from the viewpoint of global environmental protection,etc. These methods include, for example, a chemical absorption method, aphysical adsorption method, a membrane separation method, and the like.

A chemical absorption method is a method in which carbon dioxide isseparated and recovered by making use of properties of an amineabsorbing solution which absorbs carbon dioxide at 40° C. to 50° C. andreleases carbon dioxide at 100° C. to 120° C. The physical adsorptionmethod is a method in which carbon dioxide is separated and recovered bymaking use of properties of zeolite that absorbs carbon dioxide when apressure is applied and desorbs carbon dioxide when the pressure isreduced. Moreover, the membrane separation method is a method in whichcarbon dioxide is subjected to membrane-separation by use of a poroushollow fiber membrane.

However, the chemical absorption method or the physical adsorptionmethod needs the reproduction of an absorbent and an adsorbent, andconsume a large amount of energy as well. As such, it is not necessarilysuitable as a method of separating carbon dioxide for fixing carbondioxide.

On the other hand, the membrane separation method is a separation methodbased on the molecular size. However, because the nitrogen molecule andthe carbon dioxide molecule included in combustion exhaust gas havesubstantially the same size, the two kinds of molecules are difficult toseparate by this method. Moreover, it is also said that the purity ofthe recovered carbon dioxide is low.

Moreover, a method of separating carbon dioxide with gas hydrate isproposed (e.g., Japanese patent application Kokai publication No.2001-96133 and Japanese patent application Kokai publication No. Hei5-38429).

However, the method of separating carbon dioxide with gas hydrate, inany case, has difficulty in generating gas hydrate includinghigh-concentration carbon dioxide from exhaust gas with a small contentof carbon dioxide such as gas turbine exhaust gas.

DISCLOSURE OF THE INVENTION

Incidentally, the study on gas hydrates shows, for example, that carbondioxide can be concentrated by approximately 60% to 80% in carbondioxide hydrate generated at a low temperature of −70° C. to −100° C. Itis also ascertained in a bench-scale experiment.

This invention has been made on the basis of the research andexperimental results. The present invention is directed to provide amethod of recovering carbon dioxide and an apparatus therefor thatconsume a less amount of energy by improving gas hydrate formationreaction that generally shows an extremely low production rate at a lowtemperature and by effectively making use of unused cold energy wastedwhen LNG used as a fuel is gasified in gas-turbine combined cycle powerfacilities.

To achieve the above object, the present invention is constituted asfollows. The invention according to claim 1 is a method of recoveringcarbon dioxide from exhaust gas by gas-hydrating the carbon dioxide. Themethod includes the steps of: cooling the exhaust gas to a giventemperature by use of cold energy of liquefied natural gas; sprayingwater in a minute-ice generator having been cooled to a giventemperature by use of the cold energy of the liquefied natural gas togenerate minute ice; and introducing the minute ice and the cooledexhaust gas into a gas hydrate generator so as to cause the minute iceand carbon dioxide in the exhaust gas to react with each other in thegas hydrate generator, thereby generating carbon dioxide hydrate.

According to this method of recovering carbon dioxide, it becomespossible to gas-hydrate minute ice including the core of the minute icein a relatively short time by forming the minute ice (e.g., 0.1 μm to 10μm) from ice that has been said to be difficult to be gas-hydrated at alow temperature of, for example, −70° C. to −100° C. As a result, carbondioxide can be recovered efficiently from exhaust gas, particularly,even from gas turbine exhaust gas having a low content of carbon dioxide(e.g., 3% to 4%).

In addition, according to this method, by recovering unused cold energywasted when LNG is gasified and by effectively making use of the coldenergy, it becomes possible to efficiently recover carbon dioxidehydrate with a novel method that allows less energy consumption thanthat with conventional methods.

The invention according to claim 2 is the method of separating andrecovering carbon dioxide from exhaust gas, characterized in that, inclaim 1, exhaust gas cooled to approximately −70° C. to −100° C. by useof the cold energy of the liquefied natural gas is caused to contactwith minute ice having a particle diameter of approximately 0.1 μm to 10μm to thereby generate carbon dioxide hydrate.

According to this method, as described in the invention according toclaim 1, it becomes possible to efficiently recover carbon dioxide evenfrom gas turbine exhaust gas that is said to have a low content ofcarbon dioxide.

In addition, according to this method, by recovering unused cold energywasted when LNG is gasified and by effectively making use of the coldenergy, it becomes possible to efficiently recover carbon dioxidehydrate with a novel method that allows less energy consumption thanthat with conventional methods.

On the other hand, the invention according to claim 3 is an apparatus ofrecovering carbon dioxide from exhaust gas by gas-hydrating the carbondioxide. The apparatus includes: a spray nozzle; a minute-ice generatorwhich freezes particulate droplets of water sprayed from the spraynozzle by use of cold energy of liquefied natural gas to generate minuteice; and a gas hydrate generator into which the minute ice and exhaustgas cooled by use of the cold energy of the liquefied natural gas areintroduced to generate carbon dioxide hydrate.

According to this invention, as in the invention of the method, itbecomes possible to gas-hydrate minute ice including the core of theminute ice in a relatively short time by forming the minute ice from icethat has been said to be difficult to be gas-hydrated at a lowtemperature of, for example, −70° C. to −100° C. As a result, carbondioxide can be recovered efficiently from exhaust gas, particularly,even from gas turbine exhaust gas having approximately 3% to 4% contentof carbon dioxide.

In addition, according to this apparatus, by recovering unused coldenergy wasted when LNG is gasified and by effectively making use of thecold energy, it becomes possible to efficiently recover carbon dioxidehydrate with a novel apparatus that allows less energy consumption thanthat with conventional methods.

The invention according to claim 4 is the apparatus of recovering carbondioxide from exhaust gas, characterized in that, in claim 3, the exhaustgas in the gas hydrate generator is circulated between the gas hydrategenerator and a circulating-gas cooler outside the gas hydrategenerator, and that the exhaust gas is cooled by the circulating-gascooler which makes use of the cold energy of the liquefied natural gas.

According to this invention, it becomes possible to keep the inside ofthe gas hydrate generator at a given temperature, and to promote thegeneration of gas hydrate in the gas hydrate generator.

The invention according to claim 5 is the apparatus of recovering carbondioxide in exhaust gas, characterized in that, in claim 3, reaction heatgenerated in the gas hydrate generator is removed by using the exhaustgas cooled by use of the cold energy of the liquefied natural gas.

According to this invention, it becomes possible to improve the reactionbetween carbon dioxide in exhaust gas and minute and to efficientlygenerate carbon dioxide hydrate.

The invention according to claim 6 is an apparatus of recovering carbondioxide from exhaust gas. The apparatus includes: an exhaust gasprecooler which precools exhaust gas by using low temperature-lowpressure exhaust gas that has been depressurized to near an atmosphericpressure after carbon dioxide separation and recovery; an exhaust gascompressor which pressurizes the low temperature exhaust gas precooledby the exhaust gas precooler to a pressure necessary for gas hydrategeneration; an exhaust gas recooler which recools the exhaust gascompressed by the exhaust gas compressor by use of low temperature-highpressure exhaust gas after the carbon dioxide separation and recovery;an exhaust gas expander which expands the high pressure exhaust gas upto an atmospheric pressure, the exhaust gas having been subjected to arise in temperature by the exhaust gas recooler; and a gas hydrategenerating device. The gas hydrate generating device includes: ageneration water pump which pressurizes generation water up to apressure necessary for reaction; an assist gas compressor whichpressurizes part of the exhaust gas up to an assist gas pressurenecessary for spraying of the generation water; a spray nozzle whichatomizes the generation water introduced therein together with assistgas; a minute-ice generator which generates minute ice by freezing thedroplets of water atomized by the spray nozzle by use of cold energy ofliquefied natural gas; a gas hydrate generator made up of multiplereaction vessels which are connected to each other meanderingly, and inwhich the minute ice and exhaust gas cooled by use of the cold energy ofthe liquefied natural gas are introduced; an exhaust gas circulationloop which substantially circularly connects the reaction vessels toeach other through communication tubes; and a circulating-gas coolerwhich cools the exhaust gas circulating in the multiple reaction vesselswith the liquefied natural gas.

According to this invention, as in the invention of the method, itbecomes possible to gas-hydrate minute ice including the core of theminute ice in a relatively short time by forming the minute ice from icethat has been said to be difficult to be gas-hydrated at a lowtemperature of, for example, −70° C. to −100° C. As a result, carbondioxide can be recovered efficiently from exhaust gas, particularly,even from gas turbine exhaust gas having approximately 3% to 4% contentof carbon dioxide.

In addition, according to this apparatus, by recovering unused coldenergy wasted when LNG is gasified and by effectively making use of thecold energy, it becomes possible to efficiently recover carbon dioxidehydrate with novel means that allows less energy consumption than thatwith conventional methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system flow chart of a method of separating and recoveringcarbon dioxide according to the present invention.

FIG. 2 is a block diagram of an apparatus of separating and recoveringcarbon dioxide according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereafter, an embodiment of the present invention will be described withreference to the drawings.

In addition, in this embodiment, a gas-turbine combined cycle powerplant is shown as an example of an exhaust gas source origin; however,the exhaust gas source origin is not limited to this example.

As shown in FIG. 1, a facility that carries out a method of separatingand recovering carbon dioxide according to the present inventionprimarily includes a gas-turbine combined cycle power plant 10, anexhaust gas precooler 11, an exhaust gas compressor 12, an exhaust gasrecooler 13, a carbon dioxide hydrate generating device (also called,“carbon dioxide separation and recovery device”) 14 and an exhaust gasexpander 15.

In addition, in FIG. 1, the arrow of a single line shows the flow ofexhaust gas before carbon dioxide separation and recovery, and the arrowof double lines shows the flow of exhaust gas after carbon dioxideseparation and recovery.

Exhaust gas 1 a (carbon dioxide content: 3% to 4%, temperature:approximately 100° C., and pressure: approximately 0.1 MPa) dischargedfrom the gas-turbine combined cycle power plant 10 is precooled to agiven temperature by the exhaust gas precooler 11. For the precooling ofthis exhaust gas 1 a, low temperature-low pressure exhaust gas 1 e aftercarbon dioxide separation and recovery is used. The pressure of theexhaust gas 1 e has been reduced to near the atmospheric pressure (e.g.,0.1 MPa) by the exhaust gas expander 15 after discharged from the carbondioxide hydrate generating device 14.

Low temperature-low pressure exhaust gas 1 c after precooled by theexhaust gas precooler 11 is pressurized by the exhaust gas compressor 12to a pressure (e.g., 2 MPa) necessary for gas hydrate generation.Exhaust gas 1 d pressurized by the exhaust gas compressor 12 isintroduced into the exhaust gas recooler 13, and then recooled with highpressure-low temperature (e.g., 2 MPa and approximately −70° C.) exhaustgas 1 b that is discharged from the carbon dioxide hydrate generatingdevice 14 after carbon dioxide separation and recovery.

High pressure-low temperature (e.g., 2 MPa and −70° C.) exhaust gas 1 frecooled by the exhaust gas recooler 13 reacts with minute ice generatedby utilization of cold energy of LNG and becomes carbon dioxide hydratec. Reference symbol w indicates generation water for minute icemanufacturing.

As a result, carbon dioxide in the exhaust gas is incorporated into thecarbon dioxide hydrate c by 60% to 80% relative to the carbon dioxidehydrate c. Therefore, the concentration of carbon dioxide in exhaust gas1 g discharged from a chimney 16 is decreased by the amount. The exhaustgas 1 g after carbon dioxide separation and recovery is subjected to arise in temperature in the exhaust gas recooler 15 and is emitted to theatmosphere through the chimney 16.

Next, the carbon dioxide separation and recovery device according to thepresent invention will be described with reference to FIG. 2.

This carbon dioxide separation and recovery device includes thegas-turbine combined cycle power plant 10, the exhaust gas precooler 11,the exhaust gas compressor 12, the exhaust gas recooler 13, the carbondioxide hydrate generating device 14 and the exhaust gas expander 15.

Additionally, the carbon dioxide hydrate generating device 14 includes ageneration water pump 20, an assist gas compressor 21, a two-fluid spraynozzle 22, a minute-ice generator 23, a gas hydrate generator 24, anexhaust gas circulation loop 25, and a circulating-gas cooler 26 thatutilizes cold energy of LNG.

On the other hand, an exhaust gas supply pipe 28 is connected to theexhaust gas circulation loop 25 through the exhaust gas precooler 11,the exhaust gas compressor 12 and the exhaust gas recooler 13. Theexhaust gas supply pipe 28 supplies the carbon dioxide hydrategenerating device 14 with the exhaust gas 1 a discharged from thegas-turbine combined cycle power'plant 10.

In addition, a branch pipe 29 branched from the exhaust gas supply pipe28 reaches the two-fluid spray nozzle 22 in the minute-ice generator 23through the assist gas compressor 21. Moreover, an exhaust gas dischargepipe 30 that is connected to the exhaust gas circulation loop 25 isconnected to an unillustrated chimney through the exhaust gas recooler13, the exhaust gas expander 15 and the exhaust gas precooler 11.

Additionally, a water supply pipe 31 is connected to the two-fluid spraynozzle 22 in the minute-ice generator 23. In addition, a water recoverypipe 32 that recovers water generated in the exhaust gas precooler 11 isconnected to the water supply pipe 31.

Moreover, the gas-turbine combined cycle power plant 10 comprises anelectrical generator 35, a suction compressor 36, an exhaust gasexpander 37, a combustor 38 and a waste-heat boiler 39. In addition, theelectrical generator 35 is driven by the exhaust gas expander 37, andthereby electricity is generated by the electrical generator 17.

Exhaust gas discharged from the exhaust gas expander 37 in thegas-turbine combined cycle power plant 10 becomes the lowtemperature-normal pressure (e.g., 373 K (100° C.) and 0.1 MPa) exhaustgas 1 a after thermal recovery by the waste-heat boiler 39, and issupplied to the exhaust gas precooler 11.

The exhaust gas 1 a supplied to this exhaust gas precooler 11 isprecooled by using the low temperature-low pressure exhaust gas 1 e thathas been subjected to carbon dioxide separation and recovery. Thisexhaust gas 1 e is a low temperature-low pressure gas discharged fromthe carbon dioxide hydrate generating device 14, and depressurized downto near the atmospheric pressure (e.g., 0.1 MPa) by the exhaust gasexpander 15.

The low temperature exhaust gas 1 c precooled (for example, −40° C. to−50° C.) by the exhaust gas precooler 11 is pressurized using theexhaust gas compressor 12 to a pressure (e.g., 2 MPa) necessary for thegeneration of gas hydrate.

The exhaust gas 1 d compressed by the exhaust gas compressor 12 isintroduced into the exhaust gas recooler 13, and then recooled with lowtemperature-high pressure (e.g., 203 K (−70° C.), 2 MPa) exhaust gas 1 bthat is discharged from the carbon dioxide hydrate generating device 14described below after carbon dioxide separation and recovery.

After the low temperature-high pressure exhaust gas 1 b recools theexhaust gas 1 d pressurized by the exhaust gas compressor 12, theexhaust gas 1 b is emitted to the atmosphere from an unillustratedchimney via the exhaust gas expander 15. The pressure of the gas 1 gemitted at this point is approximately, for example, 0.1 MPa.

In addition, in the present invention, the exhaust gas compressor 12 andthe electrical generator 17 are driven by the exhaust gas expander 15,and electricity is generated by the electrical generator 17.

The carbon dioxide hydrate generating device 14, as already described,includes the generation water pump 20, the assist gas compressor 21, thetwo-fluid spray nozzle 22, the minute-ice generator 23, the gas hydrategenerator 24, the exhaust gas circulation loop 25 and thecirculating-gas cooler 26.

The generation water w for carbon dioxide hydrate generation ispressurized by the generation water pump 20 up to a pressure necessaryfor reaction. On the other hand, part of the exhaust gas 1 f recooled bythe exhaust gas recooler 13 is pressurized by the assist gas compressor21 up to an assist gas pressure (e.g., 2.3 MPa) necessary for sprayingof the generation water w.

The minute-ice generator 23 includes the two-fluid spray nozzle 22. Thistwo-fluid spray nozzle 22 sprays the generation water w in a particulateform from a nozzle hole (unillustrated) with the valve opened by theintroduction of assist gas 1 h.

In addition, this minute-ice generator 23 has a cooling jacket 27 on itsoutside, and instantaneously freezes the particulate water sprayed fromthe spray nozzle 22 by use of cold energy of LNG (liquefied natural gas)to generate minute ice (e.g., 0.1 μm to 10 μm) i.

Here, when the particle diameter of the minute ice i exceeds 10micrometers, it takes a longer period of time to gas-hydrate the minuteice i including the core of the minute ice, so that the use of theminute ice i having such a particle diameter should be avoided in theindustrial viewpoint. Additionally, the cooling jacket 27 uses, as acoolant, a coolant a cooled to a given temperature by utilization of thecold energy of LNG.

The gas hydrate generator 24 is made up of multiple reaction vessels 41a to 41 d that are arranged meanderingly. These reaction vessels 41 a to41 d seem to be arranged in parallel at a glance, but they are connectedsubstantially in series.

Specifically, the left end part (upstream end) of the reaction vessel 41a on the top row is connected to the outlet of the minute-ice generator23 through a communication tube 42 a. The right end part (downstreamend) of the reaction vessel 41 a on the top row communicates with theright end part (upstream end) of the reaction vessel 41 b on the secondrow through a communication tube 42. Moreover, the left end part(downstream end) of the reaction vessel 41 b on the second rowcommunicates with the left end part (upstream end) of the reactionvessel 41 c on the third row through a communication tube 42. Inaddition, the right end part (downstream end) of the reaction vessel 41c on the third row communicates with the right end part (upstream end)of the reaction vessel 41 d on the fourth row (lowest row) through acommunication tube 42. Additionally, the reaction vessel 41 d on thelowest row includes a discharge pipe 43 on its left end part (downstreamend).

On the other hand, the exhaust gas circulation loop 25 makes the exhaustgas 1 f circulate along the multiple reaction vessels 41 a to 41 ddescribed above. One end of a piping 45 for circulation loop formationis connected to the left end part of the reaction vessel 41 a on the toprow, and the other end is connected to the right end part of thereaction vessel 41 d on the lowest row. In addition, the reaction vessel41 a on the top row and the reaction vessel 41 b on the second rowcommunicate with each other on their left end parts through acommunication tube 46 a. The reaction vessel 41 b on the second row andthe reaction vessel 41 c on the third row communicate with each other ontheir right end parts through a communication tube 46 b. The reactionvessel 41 c on the third row and the reaction vessel 41 d on the lowestrow communicate with each other on their left end parts through acommunication tube 46 c.

The reaction vessels 41 a to 41 d each include a stirrer 47 to stir theminute ice i in the reaction vessels 41 a to 41 d to promote thereaction of the minute ice i with the exhaust gas 1 f.

In addition, the exhaust gas 1 a (carbon dioxide content: 3% to 4%,temperature: 100° C., and pressure: 0.1 MPa) discharged from thegas-turbine combined cycle power plant 10 is introduced into the exhaustgas precooler 11, and then precooled in the exhaust gas precooler 11 byuse of the low temperature-low pressure (e.g., 0.1 MPa) exhaust gas 1 e.

The low temperature-low pressure exhaust gas 1 c (for example, −40° C.to −50° C., 0.1 MPa) after precooled by the exhaust gas precooler 11 ispressurized using the exhaust gas compressor 12 to a pressure (e.g., 2MPa) necessary for the generation of gas hydrate. The exhaust gas 1 dpressurized by the exhaust gas compressor 12 is supplied to the exhaustgas recooler 13, and recooled in the exhaust gas recooler 13 with thelow temperature-high pressure (e.g., −70° C., 2 MPa) exhaust gas 1 bthat is discharged from the exhaust gas hydrate generating device 14after carbon dioxide separation and recovery.

Part of the low temperature-high pressure (e.g., −70° C., 2 MPa) exhaustgas 1 f recooled in the exhaust gas recooler 13 is pressurized to agiven pressure (e.g., 2.3 MPa) by the assist gas compressor 21.

When this assist gas 1 f is supplied to the two-fluid spray nozzle 22,the valve or vent incorporated in the two-fluid spray nozzle 22 isopened as already described. Then, the generation water w pressurized bythe generation water pump 20 is sprayed in a particulate form within theminute-ice generator 23. This minute particulate water isinstantaneously frozen to become the minute ice i because the inside ofthe minute-ice generator 23 is cooled to a given temperature (e.g., −30°C. to −50° C.) by the cooling jacket 27.

This minute ice i is supplied to the upstream end of the reaction vessel41 a on the top row of the exhaust gas hydrate generator 24, and thentransported to the downstream end while being stirred by the stirrer 47.On the other hand, the high pressure (e.g., 2 MPa) exhaust gas 1 fsupplied to the piping 45 for loop formation from the exhaust gas supplypipe 28 is cooled to a given temperature (e.g., 203 K (−70° C.) to 173 K(−100° C.)) by the circulating-gas cooler 26 that makes use of the coldenergy of LNG (b). Then, the exhaust gas 1 f is supplied to thedownstream end of the reaction vessel 41 a on the top row.

The minute ice i is transported toward the reaction vessel 41 d on thelowest row from the reaction vessel 41 a on the top row one afteranother. The minute ice i is to be discharged, in the end, from thedischarge pipe 43 disposed in the reaction vessel 41 d on the lowest rowto the outside of the system. However, while passing through themultiple reaction vessels 41 a to 41 d in a zigzag manner, the icereacts with carbon dioxide included in the exhaust gas 1 f to becomecarbon dioxide hydrate c.

As a result, the carbon dioxide in the exhaust gas is incorporated intothis carbon dioxide hydrate c by 60% to 80% relative to the carbondioxide hydrate c. As such, the concentration of the carbon dioxide inthe exhaust gas discharged from the chimney 16 is lowered by the amount.Moreover, the reaction heat generated when the carbon dioxide in theexhaust gas reacts with the minute ice i is removed by the cold energyof the exhaust gas 1 f.

On the other hand, while the exhaust gas 1 f circulates according to thepathway of the exhaust gas circulation loop 25, part of the exhaust gas1 f is emitted to the atmosphere via the exhaust gas discharge pipe 30described above.

The invention can be applied not only to gas-turbine combined cyclepower plants, but also widely to facilities that discharge carbondioxide such as incinerators.

1. A method of recovering carbon dioxide from exhaust gas bygas-hydrating the carbon dioxide, the method comprising the steps of:cooling the exhaust gas to a given temperature by use of cold energy ofliquefied natural gas; spraying water in a minute-ice generator havingbeen cooled to a given temperature by use of the cold energy of theliquefied natural gas to generate minute ice; and introducing the minuteice and the cooled exhaust gas into a gas hydrate generator so as tocause the minute ice and carbon dioxide in the exhaust gas to react witheach other in the gas hydrate generator, thereby generating carbondioxide hydrate.
 2. The method of separating and recovering carbondioxide from exhaust gas according to claim 1, characterized in thatexhaust gas cooled to approximately −70° C. to −100° C. by use of thecold energy of the liquefied natural gas is caused to contact withminute ice having a particle diameter of approximately 0.1 μm to 10 μmto thereby generate carbon dioxide hydrate.
 3. An apparatus ofrecovering carbon dioxide from exhaust gas by gas-hydrating the carbondioxide, the apparatus comprising: a spray nozzle; a minute-icegenerator which freezes particulate droplets of water sprayed from thespray nozzle by use of cold energy of liquefied natural gas to generateminute ice; and a gas hydrate generator into which the minute ice andexhaust gas cooled by use of the cold energy of the liquefied naturalgas are introduced to generate carbon dioxide hydrate.
 4. The apparatusof recovering carbon dioxide from exhaust gas according to claim 3,characterized in that the exhaust gas in the gas hydrate generator iscirculated between the gas hydrate generator and a circulating-gascooler outside the gas hydrate generator, and the exhaust gas is cooledby the circulating-gas cooler which makes use of the cold energy of theliquefied natural gas.
 5. The apparatus of recovering carbon dioxide inexhaust gas according to claim 3, characterized in that reaction heatgenerated in the gas hydrate generator is removed by using the exhaustgas cooled by use of the cold energy of the liquefied natural gas.
 6. Anapparatus of recovering carbon dioxide from exhaust gas, the apparatuscomprising: an exhaust gas precooler which precools exhaust gas by usinglow temperature-low pressure exhaust gas that has been depressurized tonear an atmospheric pressure after carbon dioxide separation andrecovery; an exhaust gas compressor which pressurizes the lowtemperature exhaust gas precooled by the exhaust gas precooler to apressure necessary for gas hydrate generation; an exhaust gas recoolerwhich recools the exhaust gas compressed by the exhaust gas compressorby use of low temperature-high pressure exhaust gas after the carbondioxide separation and recovery; an exhaust gas expander which expandsthe high pressure exhaust gas up to an atmospheric pressure, the exhaustgas having been subjected to a rise in temperature by the exhaust gasrecooler; and a gas hydrate generating device, wherein the gas hydrategenerating device includes: a generation water pump which pressurizesgeneration water up to a pressure necessary for reaction; an assist gascompressor which pressurizes part of the exhaust gas up to an assist gaspressure necessary for spraying of the generation water; a spray nozzlewhich atomizes the generation water introduced therein together withassist gas; a minute-ice generator which generates minute ice byfreezing the droplets of water atomized by the spray nozzle by use ofcold energy of liquefied natural gas; a gas hydrate generator made up ofa plurality of reaction vessels which are connected to each othermeanderingly, and in which the minute ice and exhaust gas cooled by useof the cold energy of the liquefied natural gas are introduced; anexhaust gas circulation loop which substantially circularly connects thereaction vessels to each other through communication tubes; and acirculating-gas cooler which cools the exhaust gas circulating in theplurality of reaction vessels with the liquefied natural gas.